Bahrdt, J.; Frentrup, W.; Grimmer, S.; Kuhn, C.; Rethfeldt, C.; Scheer, M.; Schulz, B.: In-Vacuum APPLE II Undulator. In: Shane Koscielniak ... [Ed.] : IPAC2018 : Proceedings of the 9th International Particle Accelerator Conference, Vancouver, BC, Canada. Geneve. JaCoW, 2018. - ISBN 978-3-95450-184-7, p. THPMF031/4114-4116
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APPLE II undulators are widely used in many synchrotron radiation facilities for the generation of arbitrarily polarized light, because they provide the highest magnet fields among all planar variably polarizing permanent magnet undulators (PMUs). So far, in-vacuum permanent magnet undulators (IVUs) have a fixed polarization, either planar or elliptical / helical. A variably polarizing in-vacuum undulator was never built due to the engineering challenges. We present the design of a new invacuum APPLE II, which will extend the photon energy range to tender X-rays in the 1.7 GeV storage ring BESSY II.